We plan to clarify the functions of the juxtaglomerular apparatus by studying it with light and electron microscopy in states of hypertension and sodium imbalance, particularly in conditions in which hyperplasia of agranular cells occurs independently of hypergranularity of renin-containing cells. We will study the effects of constriction of a renal artery with the opposite kidney removed and of pregnancy, low sodium diets, high sodium diets, adrenalectomy, and uninephrectomy. Electron microscopy with morphometric studies will focus on the role of agranular cells in feedback responses to sodium concentration in the distal tubule. Eventually studies will be extended to the macula densa and the renal medulla.